A variety of vessels for manipulating fluids and/or for carrying out chemical or biological reactions are available. For example, biological materials such as mammalian, plant or insect cells and microbial cultures can be processed using traditional or disposable bioreactors. Although such bioreactors and other fluid manipulating systems incorporating temperature control systems are known, there is a need for improvements to such systems, especially for microbial bioreactors.
Because microbial cultures grow and multiply twenty to forty (20 to 40) times faster than mammalian cells, both the oxygen consumption and the heat evolution rates of a microbial cultures are about 20 to 40 times greater than that of mammalian fermentation processes. In order to sustain growth in microbial cultures, the bioreactor for microbial systems must therefore be able to supply oxygen to the culture fluid and remove heat from the culture fluid 20 to 40 times faster than the oxygen supply and heat removal rates for mammalian cell cultures. This is accomplished in stainless steel microbial fermentors through a number of means, including, e.g., very vigorous agitation by multiple impellers to disperse air bubbles and increase absorption of oxygen by the cells; very high flow rates of air to supply more oxygen; extra cooling surfaces such as cooling coils to remove from the culture fluid the large amount of heat that is generated by the metabolism of the microbial cells and by the frictional heat generated by the vigorous agitation. However, in single-use bioprocessing bags, heat removal is an ongoing problem, especially for microbial bioreactors.
As is well known by those of skill in the field of polymeric or plastic materials such as films and flexible bags, polymeric or plastic films are relatively very poor conductors of heat. Therefore, cooling a fluid inside a vessel containing a replaceable container, e.g., a flexible plastic bag, may require specific modification of the cooling surfaces of the flexible bag and/or the vessel. There is an ongoing need for systems and methods to improve the removal of the large amount of heat generated by microbial cell cultures.